Lincoln was anti-slavery in the sense that he thought it was morally wrong, he just didn't see any way of ending it that was constitutional.
At the time, there was a balance of power between free and slave states. Ending that balance meant effectively the game was over, it was just going to take a while to play out. The people of the time understood the implications and acted based on their understanding.
I think that is the general consensus of Lincoln's thoughts at the beginning of his administration.
>...Ending that balance meant effectively the game was over,
Well it is debatable that the "balance of power between free and slave states" had shifted because Lincoln had been elected.
>...The people of the time understood the implications and acted based on their understanding.
Slavery had existed in many other countries. As other countries have shown, just because slavery is prohibited, that doesn't mean you need to rebel against your country and cause hundreds of thousands of unnecessary deaths.